Two cases of children with closed myelodysplasia, Arnold-Chiari malfor
mation, and shunted hydrocephalus who underwent spinal arachnoid cysto
pleural shunting are presented. Postoperatively, both patients develop
ed craniovertebral symptomatology accompanied by radiologically docume
nted ventricular dilation in spite of negative intracranial pressure a
nd functional ventriculoperitoneal (VP) shunts. Both patients recovere
d after the cystopleural shunts were revised to increase the resistanc
e to flow within the system. The authors believe that some communicati
on between the arachnoid cyst and the subarachnoid space existed in bo
th cases and that the negative pleural pressure was transmitted prefer
entially to the spinal and cerebral convexity subarachnoid spaces with
relative sparing of the ventricular system. A transmantle pressure gr
adient was thereby established, leading to ventricular dilation. The a
uthors further suggest that a craniospinal gradient was possibly estab
lished as well, leading to craniovertebral symptomatology in the patie
nts. Return of flow in the VP shunts was obtained by correcting this i
atrogenic transmantle pressure gradient.